A terahertz super surface integrating absorption, transmission and reflection and a preparation method thereof

Abstract

The application discloses a multifunctional terahertz super surface integrating absorption, transmission and reflection and a preparation method thereof, which comprises the design of a GST layer, a TOPAS layer, a vanadium dioxide layer and a graphene multilayer structure; the structure design of GST and vanadium dioxide double temperature control and graphene electric control; and the specific hollow design of the graphene layer. The application uses various tunable materials including GST, and through the control of temperature and voltage, the super surface can realize various working modes including absorption mode, transmission mode and reflection mode in the terahertz wave band. In the absorption mode, the average absorption rate of more than 95% can be realized in the 1.60-2.58 THz wave band; in the transmission mode, the average transmission rate can reach 81%; and in the reflection mode, the average reflection rate can reach 93%. The application can effectively solve the problem that the current absorber can only work in a single mode, and opens up a new road for the multifunctionalization of devices in the terahertz wave absorption field.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave manipulation, specifically to a multifunctional terahertz metasurface that integrates absorption, transmission, and reflection, and its preparation method. Background Technology

[0002] Metasurfaces, as the two-dimensional counterpart of metamaterials, are ultrathin artificial materials composed of subwavelength elements arranged in a periodic configuration, providing powerful capabilities for manipulating electromagnetic waves. Compared to traditional bulky metamaterials, metasurfaces offer advantages such as compact size, minimal loss, and ease of fabrication. Through careful design of their unit cell structures, these metasurfaces facilitate multifunctional control of electromagnetic waves, including modulation of parameters such as amplitude, frequency, phase, and polarization. Therefore, metasurfaces have been successfully applied in various fields, including planar lenses, holography, optical cloaking, and beam shaping.

[0003] Generally, metasurfaces can be classified into three operating types: transmission, absorption, and reflection. In recent years, many multifunctional metasurfaces based on these three types have been proposed in the terahertz and microwave bands, exhibiting different functions for different incident waves. However, these devices rely on the control of predetermined operating modes (absorption, transmission, or reflection), such as phase, frequency, and amplitude, without achieving mode switching, which greatly limits the further application of metasurfaces.

[0004] Dynamic and wide-range modulation of transmission, absorption, and reflection modes within a single metasurface is promising and in high demand, particularly for applications such as smart radar arrays. Currently, the main strategy for switching operating modes is to integrate active components such as PIN diodes and varactor diodes into the metasurface to achieve powerful manipulation capabilities. For example, Li et al. proposed a switchable metasurface integrating PIN diodes that achieves near-perfect absorption and transmission. Wang et al. proposed a programmable metasurface that can adjust the transmission, absorption, and reflection of electromagnetic waves in real time. However, the integration of diodes into the metasurface requires extremely high precision in processing and manufacturing, which limits the practical application of the metasurface. Another approach is to combine the metasurface with tunable materials (such as graphene, GST, Dirac half-metals, vanadium dioxide, etc.) to achieve absorption mode switching by tuning the tunable material. Liu et al. proposed a vanadium dioxide-based switchable metasurface that can switch between absorption and reflection modes at specific frequencies, but truly dynamic and wide-range operating mode switching has not yet been achieved.

[0005] To address the aforementioned issues, this invention proposes a multifunctional terahertz metasurface that integrates absorption, transmission, and reflection, in order to meet the current demand for such broadband metasurfaces in the terahertz wave field. Summary of the Invention

[0006] In order to achieve multifunctional manipulation of terahertz waves, this invention proposes a multifunctional terahertz metasurface structure that integrates absorption, transmission, and reflection. The proposed structure, while having a large bandwidth, can also achieve independent control of the operating mode, which can effectively solve the problem that current terahertz metasurfaces cannot selectively manipulate incident waves.

[0007] The technical solution of this invention is as follows:

[0008] The structure of a multifunctional terahertz metasurface that integrates absorption, transmission, and reflection.

[0009] It consists of several structural units arranged in a row. Each structural unit includes, from top to bottom: GST layer 1, used for selective emission or transmission of terahertz waves; graphene layer 2, used for regulating the absorption of terahertz waves; dielectric layer 3, used for the absorption of terahertz waves; and vanadium dioxide layer 4, used for manipulating the absorption or transmission of terahertz waves.

[0010] It also includes: a temperature controller 5, used to regulate the temperature of the GST layer 1 and the vanadium dioxide layer 4; and an external bias voltage 6, used to regulate the chemical potential of the graphene layer.

[0011] Furthermore, the cross-section of the structural unit is square.

[0012] Furthermore, the graphene layer 2 adopts an outer "mouth" and inner "rice" shaped hollow structure. Specifically, each structural unit contains an X-shaped graphene and eight isosceles right-angled triangular graphenes. The X-shaped graphenes serve as the diagonals of a square, and they are spliced ​​together to form a square. The four vertices of the square are not hollowed out. Two triangles are symmetrically arranged in each V-shaped space of the X-shaped diagonal, and the hypotenuses of the two triangles are directly opposite the X-shaped diagonal. There is a gap d3 between the adjacent right-angled sides of the two isosceles triangles in each V-shaped space. There is a horizontal or vertical gap d5 between the hypotenuse of each triangular graphene and the X-shaped graphene. There is a gap d4 between each triangle and the edge of the structural unit. These gaps form the outer "mouth" and inner "rice" shaped hollow structure.

[0013] Furthermore, the right-angled side length of each isosceles triangular graphene is d1=8.2μm, the horizontal or vertical width of the X-shaped graphene is d2=1.0μm, the gap between adjacent right-angled sides of two isosceles triangles is d3=0.6μm, the gap between the triangle and the edge of the structural unit is d4=0.3μm, there is a horizontal or vertical gap d5=0.5μm between the hypotenuse of each triangular graphene and the X-shaped graphene, and the side length of the square is equal to 20.0μm.

[0014] Furthermore, the GST layer 1 and the vanadium dioxide layer 4 are made of Ge2Sb2Te5 and VO2, respectively, and both have a thickness of 1.0 μm.

[0015] Furthermore, the dielectric layer 3 is made of cyclic olefin copolymer (TOPAS) with a refractive index of 1.53 and a thickness of 18.0 μm.

[0016] Furthermore, the temperature controller 5 has an adjustment range of 60-180℃, and the external bias voltage 6 has an adjustment range of (0-15V).

[0017] The beneficial effects of this invention are:

[0018] 1. The metasurface described in this invention solves the problem that the absorption bandwidth of current terahertz metasurfaces is still relatively small, achieving large bandwidth absorption.

[0019] 2. The metasurface described in this invention solves the problem of the untunable operating modes of current terahertz metasurfaces, achieving controllable operating modes and integrating transmission, absorption, and reflection. In absorption mode, it can achieve an average absorption rate of over 95% in the 1.60–2.58 THz band; in transmission mode, the average transmittance can reach 81%; and in reflection mode, the average reflectance can reach 93%. This invention effectively solves the problem that current metasurfaces can only operate in a single mode, opening a new path for the multifunctionality of devices in the terahertz field. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the multifunctional terahertz metasurface that integrates absorption, transmission, and reflection proposed in this invention.

[0021] Figure 2 This is a schematic diagram of a structural unit of a multifunctional terahertz metasurface integrating absorption, transmission, and reflection proposed in this invention. 1. GST layer; 2. Graphene layer; 3. TOPAS dielectric layer; 4. Vanadium dioxide layer; 5. Temperature controller; 6. Applied bias voltage.

[0022] Figure 3 This is a schematic diagram of the structural parameters of the structural unit proposed in this invention, wherein the period of the structural unit P = 20.0 μm, the side length of the triangular graphene d1 = 8.2 μm, the vertical side length of the "X"-shaped graphene d2 = 1.0 μm, the gap between the right-angled sides of two adjacent triangles d3 = 0.6 μm, and the distance of the triangle from the edge d4 = 0.3 μm.

[0023] Figure 4 This is a side view of the multifunctional terahertz metasurface that integrates absorption, transmission, and reflection proposed in this invention, wherein the thickness of the GST layer 1 is h1=1.0μm, the thickness of the TOPAS dielectric layer 3 is h2=18.0μm, and the thickness of the vanadium dioxide layer is h3=1.0μm.

[0024] Figure 5 The graph shows the absorptivity versus frequency in the absorption mode of the multifunctional terahertz metasurface that integrates absorption, transmission, and reflection proposed in this invention.

[0025] Figure 6 The graph shows the absorptivity versus frequency in transmission mode of the multifunctional terahertz metasurface that integrates absorption, transmission, and reflection proposed in this invention.

[0026] Figure 7 The graph shows the absorptivity versus frequency in the reflection mode of the multifunctional terahertz metasurface that integrates absorption, transmission, and reflection proposed in this invention. Detailed Implementation

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] Figure 1 The diagram shows a multifunctional terahertz metasurface that integrates absorption, transmission, and reflection. Figure 2 This is a schematic diagram of a structural unit of a multifunctional terahertz metasurface integrating absorption, transmission, and reflection proposed in this invention. It includes a GST layer 1; a graphene layer 2; a TOPAS dielectric layer 3; a vanadium dioxide layer 4; a temperature controller 5; and an applied bias voltage 6.

[0029] Figure 3 The diagram shows the structural parameters of a structural unit of the present invention. The period of the structural unit is P = 20.0 μm, the side length of the triangular graphene is d1 = 8.2 μm, the vertical side length of the "X"-shaped graphene is d2 = 1.0 μm, the gap between the right-angled sides of two adjacent triangles is d3 = 0.6 μm, and the distance from the triangle to the edge is d4 = 0.3 μm. The graphene layer 2 has an outer "mouth" and an inner "rice" shaped hollow structure design. The dielectric layer 3 is made of TOPAS material. 5 and 6 are external temperature controllers and bias voltages, enabling independent control of the temperature of GST and vanadium dioxide, as well as the chemical potential of the graphene.

[0030] Figure 4 In the graphene layer, the thickness of GST layer 1 is h1=1.0μm, the thickness of TOPAS dielectric layer 3 is h2=18.0μm, the thickness of vanadium dioxide layer is h3=1.0μm, and the thickness of graphene layer is very small, at 0.33nm.

[0031] Figure 5 , 6As shown in Figure 7, when a terahertz wave is incident, the metasurface of this invention can achieve the transmission effect of the terahertz wave at room temperature (less than 68°C) and a bias voltage of 0V. At this time, GST is in an amorphous state, vanadium dioxide is in a dielectric state, and the metasurface is in the transmission mode. When the temperature of the metasurface is raised above 68°C (below 160°C) using the temperature controller 5, the temperature exceeds the phase transition temperature of vanadium dioxide, and the dielectric state changes to a metallic state. At the same time, the external bias voltage is adjusted from 6 to 15V, and the working mode of the metasurface is switched to the absorption state, which can achieve effective absorption in the 1.60–2.58THz band. The temperature of the metasurface is further raised until it exceeds 160°C, and the bias voltage is adjusted to 0V. At this time, GST changes from an amorphous state to a crystalline state, which can reflect the incident wave, and the working mode of the metasurface is further switched to the reflection mode.

[0032] This invention provides a method for preparing a multifunctional terahertz metasurface that integrates absorption, transmission, and reflection. The method for preparing the terahertz metasurface is carried out according to the following steps:

[0033] (1) A vanadium dioxide layer of 1.0 μm thickness was deposited by electron beam evaporation to form the vanadium dioxide layer;

[0034] (2) TOPAS is spin-coated onto the surface of vanadium dioxide and baked to form the dielectric layer;

[0035] (3) Transfer the graphene layer above the TOPAS layer;

[0036] (4) Sputter zinc onto graphene to selectively remove graphene from these regions to form the graphene layer;

[0037] (5) A 1.0 μm thick GST layer is deposited on the surface of the graphene layer using electron beam evaporation to form the GST layer. This completes the fabrication of the multifunctional terahertz metasurface integrating absorption, transmission, and reflection.

[0038] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent methods or modifications that do not depart from the technology of the present invention should be included within the scope of protection of the present invention.

Claims

1. A terahertz metasurface integrating absorption, transmission, and reflection, characterized in that, It consists of several structural units arranged in a row. Each structural unit includes, from top to bottom: a GST layer (1), used for selective emission or transmission of terahertz waves; a graphene layer (2), used for regulating the absorption of terahertz waves; a dielectric layer (3), used for the absorption of terahertz waves; and a vanadium dioxide layer (4), used for manipulating the absorption or transmission of terahertz waves. It also includes: a temperature controller (5) for regulating the temperature of the GST layer (1) and the vanadium dioxide layer (4); and an external bias voltage (6) for regulating the chemical potential of the graphene layer. The cross-section of the structural unit is square; The graphene layer (2) adopts an outer "mouth" and inner "rice" shaped hollow structure, specifically: a structural unit contains an X-shaped graphene and eight isosceles right-angled triangular graphenes. The X-shaped graphene serves as the diagonal of a square. A square is formed by splicing together one X-shaped graphene and eight isosceles right-angled triangular graphenes. The four vertices of the square are not hollowed out. Two isosceles right-angled triangular graphenes are symmetrically arranged in each V-shaped space of the X-shaped diagonal. The hypotenuses of the two isosceles right-angled triangular graphenes are directly opposite the X-shaped diagonal. There is a gap d3 between the adjacent right-angled sides of the two isosceles right-angled triangular graphenes in each V-shaped space. There is a horizontal or vertical gap d5 between the hypotenuse of each isosceles right-angled triangular graphene and the X-shaped graphene. There is a gap d4 between each isosceles right-angled triangular graphene and the edge of the structural unit. The gaps form an outer "mouth" and inner "rice" shaped hollow structure. The temperature controller (5) has an adjustment range of 60-180℃, and the external bias voltage (6) has an adjustment range of 0-15V. The specific functional modes of the terahertz metasurface are as follows: When the room temperature is less than 68°C and the bias voltage is 0V, the transmission effect of terahertz waves is achieved. At this time, GST is in an amorphous state, vanadium dioxide is in a dielectric state, and the metasurface is in a transmission working mode. When the temperature of the metasurface is raised to more than 68°C but less than 160°C using a temperature controller (5), the temperature exceeds the phase transition temperature of vanadium dioxide and changes from a dielectric state to a metallic state. At the same time, the external bias voltage is adjusted from 6 to 15V to switch the working mode of the metasurface to the absorption state, achieving effective absorption in the band range of 1.60–2.58THz. The temperature of the metasurface is further increased until it exceeds 160°C, and the bias voltage is adjusted to 0V. At this time, GST changes from an amorphous state to a crystalline state, achieving reflection of the incident wave, and the working mode of the metasurface is switched to the reflection mode.

2. The terahertz metasurface integrating absorption, transmission, and reflection according to claim 1, characterized in that, The length of the right-angled side of each isosceles right-angled triangular graphene is d1 = 8.2 μm, the horizontal or vertical width of the X-shaped graphene is d2 = 1.0 μm, the gap between adjacent right-angled sides of two isosceles right-angled triangular graphenes is d3 = 0.6 μm, the gap between the isosceles right-angled triangular graphene and the edge of the structural unit is d4 = 0.3 μm, and there is a horizontal or vertical gap d5 = 0.5 μm between the hypotenuse of each isosceles right-angled triangular graphene and the X-shaped graphene.

3. The terahertz metasurface integrating absorption, transmission, and reflection according to claim 1, characterized in that, The GST layer (1) and vanadium dioxide layer (4) are made of Ge2Sb2Te5 and VO2, respectively, and both have a thickness of 1.0 μm.

4. The terahertz metasurface integrating absorption, transmission, and reflection according to claim 1, characterized in that, The dielectric layer (3) is made of cyclic olefin copolymer TOPAS with a refractive index of 1.53 and a thickness of 18.0 μm.

5. A terahertz metasurface integrating absorption, transmission, and reflection according to any one of claims 1-4, characterized in that, The structural units are arranged closely together.

6. A method for preparing a terahertz metasurface integrating absorption, transmission, and reflection, characterized in that, Includes the following steps: (1) A vanadium dioxide layer with a thickness of 1.0 μm was deposited by electron beam evaporation; (2) TOPAS is spin-coated onto the surface of vanadium dioxide and baked to form a dielectric layer; (3) Transfer the graphene layer above the TOPAS layer; (4) Sputter zinc onto graphene to selectively remove graphene to form a graphene layer; (5) A 1.0 μm thick GST layer is deposited on the surface of the graphene layer by electron beam evaporation to form a GST layer; thus, the preparation of the terahertz metasurface integrating absorption, transmission and reflection as described in any one of claims 1-5 is completed.

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